Evolution of Globular Microstructure and Rheological Properties of Stellite™ 21 Alloy after Heating to Semisolid State

Metal alloys can be successfully thixoformed in the partially liquid state if they display non-dendritic nearglobular microstructures. The article presents the development of feedstock with such non-dendritic microstructure produced through the solid-state route of strain-induced melt-activated (SIMA) method, for a Stellite 21 alloy. Stellite alloys are a range of cobalt-chromium alloys designed for wear and corrosion resistance, currently shaped by casting, powder metallurgy or forging processes, but semisolid-state processing offers the possibility of a near-net-shaping method for these alloys. In this work, sprayformed followed by extrusion samples were heated to the temperature range at which the liquid and solid phases coexist in the material and spheroidal shape solid particles in a liquid matrix were obtained as required for semisolid processing. Microstructural investigations were carried out using scanning electron microscopy (SEM) in combination with energy-dispersive spectroscopy (EDS), with a further objective of analyzing the rheological properties of Stellite 21 alloy in the semisolid state, providing results to be used for identi- fication of a processing window of temperature and viscosity ranges for thixoforming this alloy.